At present, a non-aqueous secondary battery such as a lithium ion secondary battery is generally employed as an electric source for driving small electronic devices. The non-aqueous secondary battery comprises a positive electrode, a non-aqueous electrolytic solution, and a negative electrode. The non-aqueous lithium ion secondary battery preferably comprises a positive electrode of lithium complex oxide such as LiCoO2, LiMn2O4, or LiNiO2, a non-aqueous electrolytic solution such as a solution of electrolyte in a carbonate solvent such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC), and a negative electrode of carbonaceous material or lithium metal.
The non-aqueous secondary battery preferably has good battery characteristics such as large electric discharge capacity and high electric discharge retention. However, there are observed certain problems in the known non-aqueous secondary battery. For instance, in the non-aqueous lithium ion secondary battery using a positive electrode of LiCoO2, LiMn2O4, or LiNiO2, oxidative decomposition of a portion of the non-aqueous electrolytic solution undergoes in the electric charging stage. The decomposition product disturbs electrochemical reaction so that the electric discharge capacity decreases. It is considered that the oxidative decomposition is caused in the non-aqueous solvent of the non-aqueous electrolytic solution on the interface between the positive electrode and the electrolytic solution.
Moreover, in the non-aqueous lithium ion secondary battery particularly using negative electrode of carbonaceous material of high crystallinity such as natural graphite or artificial (or synthetic) graphite, reductive decomposition of the solvent of the non-aqueous electrolytic solution undergoes on the surface of the negative electrode in the charging stage. The reductive decomposition on the negative electrode undergoes after repeated charging-discharging procedures even in the case of using ethylene carbonate (EC) which is a preferably employable solvent of the electrolytic solution.
Japanese Patent Provisional Publication No. 10-247517 describes incorporation of a phenolic oxidation inhibitor, a phosphite oxidation inhibitor, or a sulfide oxidation inhibitor into a non-aqueous electrolytic solution of a secondary battery to keep the battery from abnormal exothermic reaction caused in the case of over-charging or formation of short circuit.
Recently, the non-aqueous secondary battery is sometimes employed under very severe conditions such as that the charge-discharge procedure to reach a work voltage higher than 4.2 V, for instance 4.25 V or 4.3 V, is repeated at a high temperature such as 40° C. or higher for a long period of time.